1. Field of the Invention
The present invention generally relates to wireless communications networks, such as cellular networks. Specifically, the present invention relates to a scheduling process adapted to select a smart transmission mode to be used in a MU-MIMO-aware FDPS algorithm for LTE/LTE-A (or, more generally, for an Orthogonal Frequency-Division Multiple Access (OFDMA) system) downlink/uplink and perform QoS-aware scheduling decisions.
2. Overview of the Related Art
The evolution of wireless communication networks has experienced a significant growth in terms of diffusion and performance, and has recently brought to the standard 3GPP LTE and its evolution LTE-Advanced (“Third Generation Partnership Project Long Term Evolution Advanced”), which represent a major advance in cellular technology, as being designed to meet needs for high-speed data and media transport well into the next decades.
More particularly, the 3GPP LTE/LTE-Advanced is a highly efficient standard capable of conveying data information between a fixed-location transceiver radiating electromagnetic or radio waves over a respective land area called network cell, and typically referred to as enhanced base station or enhanced Node B (“eNodeB”), and user equipments (“UE”), e.g., user terminals, such as a cellular phones, within the network cell.
As known, the 3GPP LTE and its evolution LTE-Advanced employ advanced techniques, such as OFDMA and Multiple Input Multiple Output (MIMO) signal transmission.
The article “Downlink MIMO with Frequency-Domain Packet Scheduling for 3GPP LTE” by S.- B- Lee, S. Choudhury, A. Khoshnevis, S. Xu, and S. Lu, The 28th Conference on Computer Communications, April 2009, addresses the problem of frequency domain packet scheduling (FDPS) incorporating spatial division multiplexing (SDM) MIMO techniques on the 3GPP Long Term Evolution (LTE) downlink. This article provides for imposing the LTE MIMO constraint of selecting only one MIMO mode (spatial multiplexing or transmit diversity) per user per transmission time interval (TTI). First, the optimal MIMO mode selection (multiplexing or diversity) is addressed per user in each TTI in order to maximize the proportional fair (PF) criterion extended to frequency and spatial domains. It has been proved that the SU-MIMO (single-user MIMO) FDPS problem under the LTE requirement is NP-hard and therefore, it have been developed two approximation algorithms (one with full channel feedback and the other with partial channel feedback) with provable performance bounds. Based on 3GPP LTE system model simulations, the approximation algorithm with partial channel feedback is shown to have comparable performance to the one with full channel feedback, while significantly reducing the channel feedback overhead by nearly 50%.
The article “Evaluation for Various Resource Allocation Methods for Multiuser MIMO OFDMA Systems” by Jingon Joung and Yong H. Lee, IEEE 18th International Symposium on Personal, Indoor and Mobile Radio Communications, September 2007, discloses a simple algorithm to select user-pair and allocate frequency band for multiuser-MIMO OFDMA systems. For sake of comparison, various resource allocation algorithms, such as max-throughput, best-fit, first-fit, and random-fit algorithm, are examined with regard to the system throughput, computational complexity, and fairness among the users. Computer simulation results show that the first-fit algorithm can achieve a large reduction of computation for resource allocation as well as good fairness among users, with only a small reduction of throughput.
The article “A score-based Opportunistic Scheduler for Fading Radio Channels” by T. Bonald, Proc European Wireless, page 2, 2004 discusses different resource sharing strategies and presents some shortcomings of the classical Proportional Fair opportunistic scheduler.